We aim to determine the neural correlates of auditory fill in and the neural processing of complex sounds. Auditory fill-in refers to the ability of the auditory system to perceptually complete missing sounds that have been interrupted by a noise analogous to extracting a signal from a noisy environment. We intend to behaviorally characterize a task involving auditory fill-in rhesus macaques and humans. Our first goal is to compare human and macaque behavior on the hearing paradigm. We have piloted a task using frequency modulated tones (FMs) and interrupting broad band noise (BBN) and have preliminary data that suggests macaques may be experiencing auditory fill-in. We will conduct further behavioral experiments to lend support to this conclusion. Our second goal is to study neural responses to these stimuli in passively listening macaques. Here we will correlate behavioral performance with neural responses. These studies will also be important since it is unclear how cortical neurons, in multiple auditory fields, will respond to the complex sounds we have employed. Our third and final goal is to study neural responses as macaque subjects perform the behavioral task. This will combine the methods of our first and second goals and is a powerful technique which has been used in the visual system to relate neural responses. to behavioral decisions. We will determine the neural correlates of the behavioral task and the contribution of single neurons to decision making. This work will build on our understanding of the neural correlates of perception and the role of auditory cortical neurons in decisions, as well as to the knowledge of the processing of complex sounds.